Cisco Packet Tracer is proprietary software. While it is free, it requires a login to download. It is not legal or safe to download from third-party "deep paper" or torrent sites due to malware risks.
If you are writing a technical paper, using version 5.x (released circa 2009-2010) is not recommended because it is obsolete. Modern versions (8.x) include features critical for deep analysis: Cisco Packet Tracer is proprietary software
Warning: Cisco no longer hosts Packet Tracer 5.1 for public download. If you find an .exe file on third-party "top download" sites, you risk: Legitimate sources for Cisco software only come from
Legitimate sources for Cisco software only come from the Cisco Networking Academy. A direct search for "cisco packet tracer 5.1 network simulation software download top" will lead you to sketchy forums. We strongly recommend avoiding those. 8.x) that require modern CPUs
Version 5.1 is widely regarded as one of the most stable releases. Unlike newer versions (7.x, 8.x) that require modern CPUs, large RAM, and frequent updates, 5.1 runs smoothly on older hardware, including Windows XP, Windows 7, and even lightweight Linux distributions.